The Selectivity of Diphenylamine (DPA) in Detecting Deoxyribose Sugar in DNA

Why does Diphenylamine only react with the deoxyribose of purines?

Diphenylamine (DPA) is a chemical compound that is commonly used in biochemical assays to detect the presence of deoxyribose sugar in nucleic acids. When DPA reacts with deoxyribose, it forms a blue-green colored complex. However, DPA does not react with the ribose sugar found in RNA.

The selectivity of DPA towards the deoxyribose of purines can be explained based on the difference in the chemical structure between deoxyribose and ribose sugars

Both deoxyribose and ribose are five-carbon sugars, but they differ in their chemical composition at the 2′ carbon atom. Deoxyribose lacks an oxygen atom at the 2′ position, while ribose has an oxygen atom attached to the 2′ carbon

The absence of the oxygen atom in deoxyribose alters the chemical reactivity of the sugar. The reaction between DPA and deoxyribose likely involves an oxidation-reduction reaction, where DPA is oxidized while deoxyribose is reduced. The absence of the oxygen atom in deoxyribose makes it more susceptible to oxidation than ribose. Thus, DPA selectively reacts with deoxyribose rather than ribose

Purines, such as adenine and guanine, are nitrogenous bases that are components of DNA, which consists of deoxyribose sugar. By selectively reacting with deoxyribose, DPA can specifically identify the presence of DNA and its building blocks, the purines

In contrast, RNA contains ribose sugar and different nitrogenous bases, such as adenine, guanine, cytosine, and uracil. Since DPA does not react with ribose, it cannot be used to detect RNA specifically

In summary, Diphenylamine selectively reacts with the deoxyribose sugar of purines in DNA due to the absence of an oxygen atom at the 2′ carbon position in deoxyribose, making it more susceptible to oxidation compared to ribose. This unique chemical reactivity allows DPA to be used as a sensitive assay to detect the presence of deoxyribose and, hence, DNA

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